I feel like I've run out of logic on this one. There must be some technique that I'm missing because there is occasionally a puzzle that turns into a brick wall for me. I'm not going to guess on this one to move things along...

clue 7 says Gwendolyn is one month before Amelia, which according to your grid makes it either Gwendolyn May/Amelia June or Gwendolyn June/Amelia July. Either way, either Gwendolyn or Amelia must be June, so you can eliminate the other choices. That should help I haven't checked the rest of it or tried the puzzle myself, so I hope that works to get you the rest of the way.